There continues to be a push to reduce emissions from internal combustion engines. One manner in which emissions are generated from an internal combustion engine is when the engine is shut off. Fuel which has been released from fuel injectors, but has not been consumed prior to engine shut down, may evaporate outwardly through the intake manifold, intake air ducts, air filter, or components of the exhaust system and exhaust gas recirculation (EGR) system, thereby escaping into the atmosphere and contribute to air pollution.
Evaporative emission regulations for vehicles require the control of polluting substances (primarily hydrocarbons) from the vehicle as it sits unused. Evaporative emissions can leak out of a vehicle from many sources including the air intake system, fuel tank, and exhaust gas recirculation (EGR) system. In the past, only those from the fuel tank were captured, with carbon-filled canisters. However, with increasing emission regulations it has become necessary to expand evaporative emission capture technology to other vehicle components such as the EGR valve system and air intake system. Evaporative emissions need to be retained within the air inlet system until the powertrain is again used at which time the retention system will give up the harmful substances to be consumed and controlled through the normal exhaust emission control systems.
There are several ways to control the outward flow of pollutants from the air intake system of an automobile. One such technique is the careful shaping of the ducting and filter box. However, this method is often not sufficient to meet the regulatory requirements. Accordingly, other methods must be used such as the incorporation of systems in the air intake system that use some form of carbon or other material to absorb the pollutants during the rest cycle. When the vehicle is next started, the in-rushing air will draw the pollutants from the absorbent and direct the pollutants into the engine and/or through the normal exhaust system pollution controls. This inward air rush also regenerates the absorption systems so that they may be reused. Unfortunately, these extra absorption systems add cost, weight and complexity to a vehicle and often restrict the air flow.
In additional efforts to reduce these types of inadvertent evaporative emissions, many types of filters have been developed. Examples of filters for use in the intake system of a vehicle are found in U.S. Pat. No. 6,432,179 to Lobovsky et al. and U.S. Patent Application Publication No. U.S. 2002/0029693 to Sakakibara et al., both of which are incorporated herein by reference. The publication of Sakakibara et al. discloses several embodiments of hydrocarbon adsorbing devices having a case surrounding an inner cylinder portion. A hydrocarbon adsorbent material is provided in a chamber defined by the case and the inner cylinder portion. The inner cylinder portion has a central bore that extends through its length to permit induction air to pass therethrough, and also has windows that allow any hydrocarbons in the induction system to pass through a filter surrounding the inner cylinder portion to the hydrocarbon adsorbent material in the chamber to be adsorbed thereby.
As previously described, when the engine is not operating, fuel-based hydrocarbon emissions can diffuse back from the engine through the air intake, air induction system, exhaust system, or exhaust gas recirculation system and out to the ambient atmosphere. Some sources for these fuel-based hydrocarbon emissions include the fuel injectors, intake manifold walls, cylinders, positive crankcase ventilation system, and EGR valve.
In general, control of air intake system fugitive hydrocarbon emissions can be accomplished by placing a hydrocarbon adsorber unit within the air induction system between the ambient environment and the engine (e.g., before the throttle body). When the engine is not operating, hydrocarbon vapors that diffuse back though the air induction system will be trapped by the adsorber and not released to the ambient atmosphere. During subsequent operation of the vehicle, any hydrocarbons trapped on the adsorber unit will be desorbed and pulled into the engine where they are combusted. Devices for adsorbing hydrocarbon vapors within a vehicle's air intake system are well known in the art and include extruded carbon monoliths, carbon impregnated cloth, carbon impregnated polyurethane, and granular carbon (configured in a thin layer). These devices are usually located within the air cleaner box or air induction tube.
Furthermore, systems and methods for adsorbing uncombusted hydrocarbons in the exhaust gas stream of an automobile are also well known. These systems and methods are particularly useful for adsorbing uncombusted hydrocarbons emitted during the cold start of the automobile engine.
For example, U.S. Pat. No. 4,985,210 is directed to an exhaust gas purifying apparatus for an automobile employing a three-way catalyst with either a Y-type zeolite or a mordenite used in a hydrocarbon trap upstream of the three-way catalyst. In the embodiment of FIG. 2 of U.S. Pat. No. 4,985,210, a bed of activated carbon is disposed upstream of an adsorbent zone. A solenoid-operated valve mechanism serves to direct the exhaust gas stream either through or around the activated carbon bed, depending on the temperature of the exhaust gas stream, and then through the adsorbent zone and the three-way catalyst.
U.S. Pat. No. 5,051,244 is directed to a process for treating an engine exhaust gas stream in which the gas stream is directed through a molecular sieve in an adsorbent zone during the cold-start phase of engine operation. When the hydrocarbons begin to desorb, the adsorbent zone is by-passed until the catalyst is at its operating temperature, at which point the gas stream is again flowed through the adsorbent zone to desorb hydrocarbons and carry them to the catalyst zone. A paper by M. Heimrich, L. Smith and J. Kotowski entitled Cold-Start Hydrocarbon Collection for Advanced Exhaust Emission Control, SAE Publication Number 920847, discloses an apparatus which functions in a manner similar to that of U.S. Pat. No. 5,051,244.
U.S. Pat. No. 5,125,231 discloses an engine exhaust system for reducing hydrocarbon emissions, including the use of beta zeolites as hydrocarbon adsorbents. Zeolites having a silica/alumina ratio in the range of 70/1 to 200/1 are preferred adsorbents. The apparatus includes by-pass lines and valves to direct exhaust gases from a first converter directly to a second converter during cold-start operation and when the first converter reaches its light-off temperature, to either by-pass the second converter or recycle effluent from it to the first converter.
U.S. Pat. No. 5,158,753 discloses an exhaust gas purifying device comprising: a catalyst device installed in the exhaust gas path of an internal combustion engine for treating the exhaust gas of the engine; an adsorbing device installed in the exhaust gas path between the catalyst device and the internal combustion engine, for treating the exhaust gas of the engine. One embodiment includes a heat exchanger for performing heat transfer between the exhaust gas flowing from the internal combustion engine to the adsorbing device and the exhaust gas flowing from the adsorbing device to the catalyst device. Alternatively, the catalyst device includes a catalyst secured in the low-temperature-side gas flow path of a heat exchanger, and the exhaust gas flowing from the internal combustion engine to the adsorbing device is allowed to flow to the high-temperature-side gas flow path of the heat exchanger.
U.S. Pat. No. 6,171,556 discloses a method and apparatus for treating an exhaust gas stream containing hydrocarbons and other pollutants. The method comprises the steps of flowing the exhaust gas stream through a catalytic member comprising a monolith body having a first catalyst zone and a second catalyst zone therein to contact a catalyst in a first catalyst zone to convert at least some of the pollutants in the exhaust gas stream into innocuous products. The exhaust gas stream is then discharged from the catalytic member and flowed through an adsorbent zone to adsorb at least some of the hydrocarbon pollutants with an adsorbent composition. The exhaust gas stream is discharged from the adsorbent zone and flowed to the second catalyst zone to convert at least some of the pollutants into innocuous products. The exhaust gas stream, so treated, is then discharged to the atmosphere through suitable discharge means. A preferred adsorbent is a zeolite, having a relatively high silica to alumina ratio and a low relative Bronsted acidity. The preferred adsorbent compositions comprise beta zeolites.
It is also known in the art to provide an automobile internal combustion engine with an exhaust gas recirculation (EGR) system for the circulation of a flow of exhaust gases from the engine back to the engine. The recirculation of exhaust gas back to the engine cools the engine, and thereby, limits the formation of nitrogen oxides (NOx) in the engine (exhaust gas). The EGR system contains an EGR valve, which can be opened or closed to varying degrees, to control the flow of engine exhaust gases through the exhaust gas recirculation system. Since the EGR valve is connected to the air intake system and is vented for pressure relief, the EGR valve can be an additional route for release of hydrocarbons to the atmosphere while the vehicle engine is not in operation. Due to the large size, the prior art hydrocarbon adsorber units, described above, cannot be included in or added to the EGR valve. Therefore, it is an object of the present invention to provide a means of controlling evaporative hydrocarbon emissions from the EGR valve.
As discussed above, zeolites are often used as coatings on monolithic substrates for various high temperature adsorption and catalytic applications. In these cases, inorganic binder systems are used that survive exposure to high temperatures (e.g., >500° C.) and provide good coating adhesion. However, for low temperature application (e.g., <500° C.), inorganic type binders are often not suitable since their binding characteristics are severely diminished. In these low temperature applications, organic polymer binders are ideal since they are structurally stable and provide excellent coating adhesion.
For example, commonly assigned U.S. Patent Publication No. 2004/0226440 discloses a hydrocarbon adsorption unit. The unit is positioned in the air intake system and has an air intake and air outlet. According to the application the adsorber material may be silica gel, a molecular sieve and/or activated carbon and contains an organic polymer binder, as well as an anionic, nonionic or cationic dispersant, that will cause the material to adhere to the surface of a substrate.
However, without proper choice of these stabilizing agents, interparticle agglomeration of zeolite particles or coagulation of zeolite and binder particles will occur, thus rendering the slurry unstable for coating application. As a result, a zeolite-based coating formulation must be developed that not only has good adhesion (particularly to metal substrates) at low temperature, but also excellent adsorption characteristics.
Therefore, it is an objective of the present invention to provide an improved exhaust gas recirculation system for controlling exhaust gas emissions from a motor vehicle's exhaust gas recirculation (EGR) system. It is another objective of the present invention to provide a hydrocarbon adsorbent slurry coating to an EGR valve to reduce hydrocarbon vapors from the exhaust gas, thereby preventing release of hydrocarbons into the ambient atmosphere. A key advantage to this invention is that existing components of the EGR valve can be coated with adsorbent without the need for significant valve redesign.